With regard to electronic devices, for example, a digital I/O unit in a sequencer system (a programmable controller) is a unit that primarily causes, for example, an input unit to transmit a signal received from an input device to a CPU unit, and an output unit to output a signal on which input/output processing has been performed in the CPU unit to an output device. In such a unit, stability of input data is important. However, when operated in an environment where noise is generated, there is a possibility of a phenomenon such that unit operations are affected, such as the occurrence of erroneous input ascribed to the effect of the noise.
As a countermeasure against noise that affects on input data, there has been proposed a technique to filter input data. In this case, the input data is sampled. If the sampled values consecutively have the same value for a predetermined number of times, then the input date is defined (see, for example, Patent Literature 1).
However, depending on the environment where devices are used, noise is generated to have a constant periodicity, for example, in places around a device having a driving motor. According to the technique described above, the timing (hereinafter, “sampling”) of which date is read has a constant interval in multiple reading operations. Thus, there is a possibility of erroneous input if the period of noise and the sampling timing match each other.